1. Field of The Invention
The invention relates to a sound reproduction system comprising a left channel and a right channel loudspeaker, a surround decoder unit for decoding at least one input signal into at least one rear surround signal and two channel stereophonic signals, a surround signal processing unit for converting the rear surround signal(s) into a first and a second surround signal and for localizing these surround signals at virtual sound sources located away from the left channel and the right channel loudspeakers, and first combining means coupled to one of the loudspeakers for combining the first surround signal with one of the stereophonic signals, and second combining means coupled to the other loudspeaker for combining the second surround signal with the other stereophonic signal, and the surround signal processing unit further comprises filter means.
The invention further relates to a surround signal processing unit.
The invention further relates to a sound/visual reproduction system comprising a sound reproduction system.
The invention further relates to a method for processing an input surround sound signal.
2. Description of The Related Art
To improve listener perceived characteristics, multi-channel sound reproduction systems are known which include a surround-sound channel (often referred to in the past as an "ambience" or "special-effects" channel) in addition to left and right (and optimally, center) sound channels. These systems are now relatively common in motion picture theatres and are becoming more and more common in the homes of the customers. A driving force behind the proliferation of such systems in consumers' homes is the widespread availability of surround-sound home video software, mainly surround-sound motion pictures (movies) made for theatrical release and subsequently transferred to home video media (e.g., videocassettes, videodisks, and broadcast or cable television).
Although home video media have two-channel stereophonic soundtracks, those two channels carry, by means of amplitude and phase matrix encoding, four channels of sound information, i.e., left, center, right and surround sound, usually identical to the two-channel stereophonic motion-pictures soundtracks from which the home video soundtracks are derived. As is also done in the motion picture theatre, the left, center, right, and surround channels are decoded and recovered by consumers with a matrix decoder, usually referred to as a "surround-sound" decoder. In the home environment, the decoder is usually incorporated in, or is an accessory to a videocassette player, videodisk player, or television set/video monitor.
In the case where stereophonic sound is reproduced in such a way as to provide a sound field expanding behind a listener or to localize a sound image behind a listener, two (front) loudspeakers are arranged in front of a listener for stereophonic sound reproduction and at least one or two rear loudspeakers are additionally arranged behind the listener for surround reproduction.
In the ordinary homes, however, since it is difficult to arrange the two rear loudspeakers and the center loudspeaker from the standpoint of space and cost, in practice, only L- and R-channel loudspeakers are installed on the front left and right sides of a listener. In this loudspeaker arrangement, it has become impossible to obtain sufficient surround sound effect. In the case of the sound reproduction system using a monophonic surround signal in particular, although this system has such a feature that a sound field can be obtained on the rear side of a listener or the sound image can be shifted, it has been impossible to obtain such effects as described above without arranging the rear loudspeakers.
To solve the above problem, it is known from the European Patent Application EP-A-0637191, corresponding to U.S. Pat. Nos. 5,579,396 and 5,761,315, to use a surround signal processing unit (apparatus) whereby a stereophonic sound effect, similar to the case where the rear loudspeakers are arranged, can be obtained on the basis of the sound reproduction through only the front left and right loudspeakers.
The inputted rear surround signal is processed by filter means and the processed signal is added to one of the stereophonic signals and then outputted to one of the pair of the loudspeakers. Further an inversion signal of the filter processed signal is added to the other of the stereophonic signals and then outputted to the other of the loudspeakers.
A disadvantage of this known sound reproduction system is that the perceived sound depends strongly on the position (of the head of the listener and) of the listener. Further, the filter characteristics are complex and dependent on the listener, for example, of the rear canal, head/torso, and/or pinna, resulting in possible failures of the requested results. Further, this known sound reproduction system is complex.